1. Field of the Invention
The present invention relates to a pump system for transferring a target fluid via a pump camber using reciprocating flexible members such bellows and diaphragms. In particular, it relates to a pump system using a control fluid to drive a switching valve mechanism for an actuating fluid.
2. Description of the Related Art
A bellows pump is known as a liquid injection pump for use in semiconductor processes and so forth in the art. It employs fluororesin bellows for sucking and discharging a liquid. The bellows pump includes a pump head containing a valve unit; a pair of bellows located at both sides of the pump head to form pump chambers inside these bellows; and a case for covering the outside of the bellows to form a pair of air chambers. When an air is supplied alternately into the air chambers to extend and contract the bellows, a target fluid such as a liquid can be transferred as it is sucked into and discharged from the pump chamber.
The air is supplied from an air source, switched at a switching valve mechanism such as a magnetic valve and fed as an actuating fluid alternately to the pair of air chambers. As for switching control of the switching valve mechanism, proximity switches are located at both ends of the case to detect a moving end of each bellows. The use of the proximity switches requires metals and wires arranged in the sensor sections. Generally, inside the pump chamber is a first liquid-contact section and the air chamber is a second liquid-contact section that is a liquid-free section. The proximity switch may be often located in the second liquid-contact section. In the case of a pump for transferring a metal-corrosive target fluid, however, it is desired to avoid the use of metals and metallic wires in the second liquid-contact section as far as possible.
In known bellows pumps of an all air type, a switching valve mechanism is switched under pressure of a fluid (control fluid) branched from the actuating fluid (U.S. Pat. No. 5,893,707 and U.S. Pat. No. 5,558,506).
The above-described bellows pumps of the all air type include one that houses a switching mechanism for switching the switching valve mechanism in a pump case as disclosed in U.S. Pat. No. 5,893,707. This rises a problem because of the poor maintenance ability for the switching mechanism and no compatibility with a switching mechanism of the proximity switch type. In the bellows pump disclosed in U.S. Pat. No. 5,558,506, as a part of a switching mechanism for switching the switching valve mechanism, a piston is fixed to a reciprocating shaft. Accordingly, the switching mechanism can not be detached and attached individually. This also rises a problem because of the poor maintenance ability for the switching mechanism and no compatibility with a switching mechanism of the proximity switch type.
The use of the proximity switch has merits because: (1) the number of reciprocating strokes of the pump can be converted into a discharged flow amount; and (2) the pump halting due to some trouble can be detected from an electric signal. Therefore, it is greatly significant to replace the switching mechanism of the all air type for the proximity switch type.